Arrangement for reducing errors resulting from signal faults or omissions



Jan. 11, 1966 M. ROSENBLATT ARRANGEMENT FOR REDUCING ERRORS RESULTINGFROM SIGNAL FAULTS OR OMISSIONS Original Filed Oct. 12. 1960 6Sheets-Sheet 1 INVENTORI MURRAY ROSENBLATT,

W HZTTQRNEY.

Jan. 11, 1966 M. ROSENBLATT ARRANGEMENT FOR REDUCING ERRORS RESULTINGFROM SIGNAL FAULTS 0R OMISSIONS Original Filed Oct. 12, 1960 6Sheets-Sheet 2 Jan. 11, 1966 M. ROSENBLATT ARRANGEMENT FOR REDUCINGERRORS RESULTING FROM SIGNAL FAULTS OR OMISSIONS Original Filed Oct. 12,1960 6 Sheets-Sheet 5 FIG.3. +aoov.

OUTPUT TO INTEGRATOR SQUARE WAVE GENERATOR D W 8 am RNHW F E N A T R N 4UEARI.

IRC

FIG.5.

INPUT Y I\ I PULSES LOST l PULSES l A I UPPER CATHODE FOLLOWERIO2 PULSESLOWER CATHODE FOLLOWERIO4 \IIIIIN PULSES UPPER CAPACITORIIO VOLTAGELOWER CAPACITOR H2 VOLTAGE UPPER MULTIVIBRATOR ANODE VOLTAGE LOWERMULTIVIBRATOR ANODE VOLTAGE Jan. 11, 1966 M. ROSENBLATT ARRANGEMENT FORREDUCING ERRORS RESULTING FROM SIGNAL FAULTS OR OMISSIONS Original FiledOct. 12. 1960 6 Sheets-Sheet 5 Om- Baum-0 mm. "-0.520: mom-mm mmwoxmJ/Hp m! mmhJE Paar-'30 m! Emma-4Q Jan. 11, 1966 M. ROSENBLATT 3,229,270

ARRANGEMENT FOR REDUCING ERRORS RESULTING FROM SIGNAL FAULTS OROMISSIONS Original Filed Oct. 12, 1960 6 Sheets-Sheet 6 IOOV. 93 FIG] 1no lNPUT FROM FILTER 14a OUTPUT'TO STABILIZING CIRCUIT r I52 C O GROUND+3oov. FlG-s OUTPUT TO I INPUT FROM fi FILTER I4 STABILIZING CIRCUIT I52kc I96 I GROUND 82 -3oov.

FIG-9 +23 ZIO OUTPUT T0 INPUT FROM FlLTE/R 148 1' STABILIZING CIRCUITI52 GROUND} r220 lNVENTOR MURRAY ROSENBLATT,

BY UM fing ATTORNEY.

United States Patent 3,229,270 ARRANGEMENT FOR REDUCING ERRORS RE-SULTING FROM SIGNAL FAULTS OR OMISSIONS Murray Rosenhlatt, Cherry Hill,NJ assignor to General Electric Company, a corporation of New'York(Iontinuation of application so. No. 62,208, Oct. 12, "1964). Thisapplication Sept. 15, 1964, Ser. No. 398,834 12 Ci'ai'ms. (Cl; 340-1741)The invention relates to improvements in programmed controI systems, andparticularly to such an improvement for reducing errors resulting fromfaults in the signals derived from the programmed information. Moreparticularly, the'invention relates to arrangements for reducing theerrors which may result from faults or omissions'in the signals providedin a programmed control system such as described in Patents Nos.2,537,770; 2,866,145; 2,894,253; and 2,922,052. This application is acontinuation of my copending application, now abandoned, entitledArrangement for Reducing Errors Resulting From Signal Faults orOmissionsffiled October 12, 1960, Serial No. 62,208. i i i As describedin these patents, the position or opera tion of a machine tool or otherdevice may be controlled in a system whichoperatesin accordance withinformation stored on a data storage medium, such as a magnetic tape.The stored information is characterized by the operations desired, andwhen this information is reproduced, the machine tool or other device'is operated or moved in accordance with this stored information toaccomplish the desired result. The stored information is reproducedthrough" suitable means when it is desired to bringabout the operationcharacterized or determined by the stored information. The systems shownin the patents provide areference signal and also provide a controlsignal for each motion or operation which it is desired to effect orbring about. Means are providedfor developing a signal whichisindicative of the true position or operation of the object beingcontrolled. The signals indicative of the true position or operation ofthe device being controlled and the control signal for each channel ormotion or operation which isbeing controlled are fed to a discriminatoror other device for developing an error signal indicative of .thedeviation between the true position or operation and the programmedposition or operation. Through suitable positioning or operating means,the error "signal is supplied to the device in order thatit may assumethe correctprogrammed operation or programmed position. On occasions,the information stored is not faithfully reproduced, 'or in'some casesit may not be reproduced at all for a brief periodof time. In thesystem, it is desirable, if not necessary,.that movement or operationcontinue during the brief fault or'absence of such stored information soas to preserve the work and continue the operation.

Accordingly, an object of the invention is to provide an arrangementwhereby a control system operating from stored information may continueoperation despite a brief fault in, or absence of the storedinformation.

Another object of the invention is to provide an arrangementfor acontrol system operatingfrom stored information which permits continuedoperation of the system despite loss of or faults in the storedinformation, the continued operation being substantially similar to theoperation priorto the loss of or-faults inthe stored information.

In addition to loss of or faults in the stored information, transientsignals arising from a number of extraneous causes and conditions may bepresent. Such transient signals may serve to introduce false operationof the control system, this false operation resulting in imperfect work,or operation. 2

Accordingly, another object of the invention is to provide anarrangement which limits the rate at which signals used in a programmedcontrol system can change.

Briefly, these and other objects of the invention are achieved in aprogrammed control system by the provision of means which respond tosignals from the storage medium and normally produce appropriate signalsin response thereto. In accordance with the invention however, thesemeans are so arranged that in the absence of signals from the storagemedium, appropriate signals will continue to'be produced for someduration of time. The means may, in accordance with the invention,'beselfsustaining and produce signals at a predetermined rate,:or they maybe so arranged that they are self-sustaining and produce signals at arate dependent upon the rate of the signals derived from the storagemedium just prior to their being lost or omitted.

In another embodiment of the invention, the programmed control system isprovided with means which limit the rate of change of signals from thestorage medium for producing the desired positioning or the desiredoperation. Thus, if signals from the storagemedium are absent or are ofsuch a characteristic, or if extraneous signals which are present andare ofsuch a characteristic that an undesirable operation, such as anincrease in speed, were to take place,the ratelimit means of theinvention limits the rate of change to some predetermined level orvaluef i The subject matter of the invention is particularly pointed outand'distinctly claimed in the concluding portion of the specification.The invention, however, both as to its arrangement and method ofoperation, together with additional'objects and advantages, may bebetter understood by reference to the following description taken inconnection with the accompanying drawing. In the drawing:

FIGURE 1 shows a block diagram of a programmed control system in whichthe invention may be used;

FIGURE'Z shows a block diagram of a selsyn exciter in which theinvention may be used, the selsyn exciter being a portion of the controlsystem shown in FIG- URE 1;

FIGURE 3 shows a circuit diagram of a square wave generator inaccordance with the invention which may be used inthe selsyn eXcitershown in FIGURE 2;'

FIGURE 4 shows a circuit diagram of a generator in accordance withanother embodiment of the invention which may be, used in the controlsystem shown in FIG- URE l;

' FIGURE 5 shows waveforms for explaining the operation of the circuitshown in FIGURE 4;

FIGURE 6 shows a block diagram of a discriminator in which the inventionmay be, used, the discriminator being aportion of the control systemshown'in FIGURE 1; and

FIGURES 7, 8, and 9 show circuit diagrams of rate limit circuits inaccordance with the invention and which maybe used in the discriminatorshown in FIGURE 6.

In FIGURE 1, there is shown a programmed control system similar to thosedisclosed in the previously mentioned patents. Sincethe system shown isdescribed in detail in the patents mentioned,,the operation will be onlybriefly described here. A storage medium 10, such as a magnetic tape,.isprovided. The storagemedium 10 is provided with a plurality of channels,only three being shown by dashed lines in the interests of clarity.However, additional channels, representing additional operations, may beprovided on the storage medium 10. Previously determined information maybe recorded on the storage medium 10, and reproduced by suitable pickupheads 12 appropriately positioned with respect to their respectivechannels. One of the pickup heads 12 is associated with a referencechannel, and the other two pickup heads 12 are associated with channelsrespectively labeled channel A and channel B. These channels A and B mayrepresent any desired operation, such as movement in mutuallyperpendicular directions. It is to be understood that the storage mediumrepresented in FIG- URE 1 as being a magnetic tape is for the purposesof illustration only, because any suitable storage device may be used.Likewise, it is possible that the arrangement shown may be used in otherapplications in addition to that shown or contemplated. Signals derivedby the pickup head 12 associated with the reference channel are appliedto a preamplifier 14, after which they are applied to a selsyn exciter16. The selsyn exciter 16 develops an output signal or signals having atleast two phases. As illustrated in FIGURE 1, output signals of threephases are derived and applied to the conductors 18 which supply thesesignals to differential selsyns 20 respectively associated with thechannels A and B. The differential selsyns 20 are, in turn, respectivelycoupled to position indicating selsyns 22. As illustrated by the dashedlines, the position indicating selsyns 22 are mechanically connected torespective positioning motors 24 which, in the example mentioned, mayprovide mechanical movement of an object 26 or objects 26 in mutuallyperpendicular directions. A motor controlled unit, such as an amplidyne28 or other power amplifier, furnishes a motor control signal, thedirection and magnitude of which is determined by the forward andreverse windings 30, 32 respectively energized by an amplidyne fieldpanel 34. While the arrangement shown is directed essentially to anelectronic and electrical positioning system, it is to be understoodthat mechanical systems, such as those of a hydraulic nature, may beused.

Control signals having predetermined phase relationships with referencesignals as provided by the storage medium 10 are derived from therespective channel A and channel B pickup heads 12 and amplified insuitable preamplifiers 36. The amplified signals are applied torespective discriminators 38, to which signals from the positionindicating selsyns 22 are also applied. These signals from the positionindicating selsyns 22 have a phase relationship with respect to thereference signals which is indicative of the true position of theobjects 26. The position indicating selsyns 22 are coupled to'thediscriminators 38 which develop error signals indicative of the phaserelationship between the signals from the position indicating selsyns 22and the signals provided by channels A and B of the storage medium 10.The error signals are applied to the respective amplidyne field panels34. Tachometers 40 are mechanically coupled to the motors 24 to furnisha velocity stabilizing signal which is also applied to the amplidynefield panels 34.

FIGURE 2 shows a block diagram ofthe selsyn exciter 16 shown inFIGURE 1. The block diagram of the selsyn exciter 16 is shown toillustrate how the invention may be used in the selsyn exciter 16. Theselsyn exciter 16 provides a plurality of sinusoidal alternating currentelectrical signals having a predetermined phase relationship withrespect to each other from the reference signals derived from thestorage medium 10. Since the selsyn exciter 16 shown in FIGURE 2 isexplained in Patent Nos. 2,894,253 and 2,922,052 in some detail, adetailed explanation of the selsyn exciter 16 will be omitted here.However, a brief explanation follows. The selsyn exciter 16 includes asquare wave generator 50 which is exemplified as being a bistablemultivibrator that is operated in response to the reference signalsderived from the storage medium 10 after amplification by thepreamplifier 14. Thus, operation of the selsyn exciter 16 ascontemplated by the patents is dependent upon the reference signalsbeing received. The reference signals derived from the storage medium 10consist of positive and negative-going pulses which are applied tothesquare wave generator 50. The square wave generator 50 producessquare or rectangular Waves in response to the pulses as shown, andthese square waves are applied to an integrator 52 which develops atriangular wave and supplies it to a wave shaper 54. The Wave shaper 54forms the integrated wave which is triangular into a substantiallysinusoidal wave and applies this sinusoidal wave to a power amplifierNo. 1 and to a phase shifter 56. The output of the phase shifter 56 isapplied to the power amplifier No. 2 through a gain control 58, thisgain control 58 receiving signals from both power amplifiers Nos. 1 and2 for the purpose of maintaining the desired relative amplitude betweenthe two sinusoidal waves applied to the power amplifiers. Afteramplification in the power amplifiers, these signals are applied toScott-connected transformers 60 which provide three-phase signals on theconductors 18. These signals are applied to the differential selsyns 20.

The square wave generator 50 which is shown in the patents mentioneddepends upon the reference signals being received. In the absence ofsuch reference signals, the square wave generators cease to function sothat no signals or unsuitable signals are provided by the selsyn exciter16. a square wave generator is provided which continues to producesquare wave pulses for a predetermined length of time even in theabsence of signals from the reference channel. FIGURE 3 shows a circuitdiagram of a square wave generator in accordance with the inventionwhich may be used with the selsyn exciter 16 shown in FIG- URE 2. Thesquare wave generator of FIGURE 3 comprises two vacuum tubes 72, 74having respective anodes, cathodes, and control grids. It is to beunderstood that other electron discharge devices, such as transistors,may be used in place of the tubes. T he anode of each of the tubes 72:,74 is coupled to the control electrode of the other tube through seriesconnected resistor-capacitor networks 76, 78. The anodes of the tubes72, 74 are appropriately connected to a +300 volts bus 80 and thecathodes of the tubes 72, 74 are appropriately connected to a 300 voltsbus 82. The buses 80, 82 supply direct current potentials which arepositive and negative with respect to a reference or ground bus 70. Thevalues of voltage shown in FIGURE 3, as well as in subsequent figures,are exemplary only, and are not intended to limit the invention in anyway. The control electrodes are connected together through a frequencydetermining p0- tentiometer 84 and are appropriately connected to the+300 volts bus 80 through resistors and through a balancingpotentiometer 86. The control electrodes are also connected to the 300volts bus 82.

The circuit of FIGURE 3 as described thus far provides, in effect, anastable or free-running multivibrator whose frequency is determined bythe values of the circuit components. In the absence of signals from thereference channel preamplifier 14, the circuit shown operates to producesquare waves at the output which is connected to the integrator 52.However, in order to make the square wave generator responsive to suchsignals when they are present, signals from the reference channelpreamplifier 14 are applied, with respect to the ground bus 70, to thecontrol electrode of one of the tubes, the lefthand tube 72, forexample. These signals are applied through a serially connected networkcomprising two resistors 88, 9t) and a capacitor 92. The input signalssupplied to the square wave generator of FIGURE 3 may take the form asshown and comprise positive and negative-going pulses. Upon receipt of apositive-going pulse, the left-hand tube 72 is turned on, with theresult that its anode potentialfalls. This fall in anode potential is applied to the control electrode of the right-hand tube 74 to cut it offso that its anode potential rises in accordance with the usualmultivibrator action. If the predetermined or normal free-runningfrequency of the multivibrator shown in FIGURE 3 is lower than thefrequency of the input signals, the next negative-going pulse from thepre- In accordance with the invention, however,

are provided at a substantially constant frequency. the caseof aninformation channel, the pulse frequency may vary in accordance .withthe information being con- FIGURE 1. frequency determined by the inputpulses supplied thereto amplifier 14 causes the left-hand tube 72 to becut off and thus its anode potential rises. This rise in anode potentialis coupled to the control electrode of the right-hand tube 74 to turn iton, with the result that its anode potential falls. Thus, the squarewave generator of FIGURE 3 provides square wave signals having afrequency which is responsive to the frequency of the incoming signals.However, in the absence of such incoming signals, the square wavegenerator continues to operate at its inherent or normal ferquencydetermined by the values of the networks 76, 78 as well as theothercircuit components. Thus, square wave signals will be provided tothe integrator 52 both in the presence of and in the absence of signalsfrom the reference channel preamplifier 14.

The problems of pulse restoration in an information channel, such aschannels A or B in FIGURE 1, are more complicated than in a referencechannel where the pulses In veyed, such as faster or slower operation ordifferent positions. Normally, however,the operation of the device beingcontrolled does not change instantly but preferably changesgradually(corresponding to some predetermined maximum rate of acceleration).Thus, the pulse frequency, although a variable, varies slowly at theinput of the discriminator 38 shown in FIGURE 1. In accordance with theinvention, a pulse generator may be provided between the channelpreamplifier'36 and the discriminator 38 of any or all of theinformation channels shown in This generator provides pulses having afrom theinformation channels. In the absence of such input pulses, thegenerator in accordance with the invention provides pulses which havesubstantially the same frequency as the inputpulses just prior to theirloss or absence, and which gradually decrease in frequency until suchtime as the pulses are again supplied. FIGURE 4 shows a circuit diagramof this generator in accordance with the invention, and FIGURE 5 showswaveforms for explaining the operation of the generator of FIGURE 4. Inthe embodiment shown in FIGURE 4, electron discharge tubes of the triodevariety areused. However, it is to be understood that other electrondischarge devices,

such as transistors, may also be used. 'Suitable potentials are providedfor the generator of FIGURE 4-by'the +300 volts bus 80, the 300 voltsbus 82, the ground bus '70, a +100 volts,bus 97, a --l0 volts bus 98,and a 100 volts bus 99. These buses supply direct current potentials ofthe magnitudes and polarities indicated with respect to the ground bus70. Pulses are supplied to an input circuit from the preamplifier 36,and are applied to the control electrode or grid of a phase splittertube Output signals from the phase splitter tube 100 are derived at itsanode and its cathode and respectively applied to the control electrodeof an upper cathode follower tube 102 and the control electrode of alower cathode follower tube 104. The outputs of the upper and lowercathode follower tubes 102, 1194 are respectively applied through anupper diode network 106 and a lower diode network 108to upper andlowertiming capacitors 110, 112 respectively. One end of the upper and lowertiming capacitors 110, 112 is coupled to the groundbus70,.andthe otherends are respectively coupled to the diode networks 1'06, 168. The otherend of the upper and lower timing capacitors 110, 112 are also coupledthrough respective potentiometers114, 116 and resistors to the 3 0 Ovolts bus 82. And, the other ends of the timing capaciand diode networksto the control electrodes of multivibrator tubes 126, 128. Themultivibrator tube 126 will be referred to as the upper multivibratortube, and the multivibrator tube 128 will 'be referred to as the lowermultivibrator tube because their control electrodes are respectivelycoupled to the upper and lower coupling tubes 126 122 and associatedcircuitry. The multivibrator tubes 126, 128 are connected as a bistablemultivibrator circuit, and hence the anode of each tube is coupledthrough a direct current path including a resistor to the controlelectrode of the other tube. Thus, when one state of conduction ispresent, that state continues until such time as an external signal isapplied to one of the control grids of the multivibrator tubes 1-2.6,128. The output signals from the generator .of FIGURE 4 are vderivedfrom the anode of the lower multivibrator tube 128 and are applied, ifdesired, through a differentiating network 130 to the control electrodeof an output cathode follower tube 134. Output signals are derived:between .thecathode of theoutput tube 134 and ground bus '70 and maybeapplied to the discriminator 38 shown in FIG- URE ,l.

The operation of the generator shown in FIGURE 4 will be explained inconnection with the Waveforms shown in FIGURE '5. In FIGURE 5, waveformsare shown as plotted against time intervals bearing the designation Tfollowed by-a subscript numeral. At some time prior to the time T it isassumed that the circuit is in operation, and that input pulsesconveying some information (such as needed to produce an operationormotion) are being supplied to the phase splitter tube 100. These pulsesare designated input pulses. A positive-going input pulse causes thecathode potential of the phase splitter tube 10tl-to rise, and causesthe anode potential of the phase splitter tube to fall. Likewise, anegative-going pulse causes the cathode potential of the phase splittertube .100 to fall and causes the anode potential of the phase splittertube 101) to rise. The upper and lower cathode follower tubes 102, 1414are normally in some stable condition as determined-by the values of thecircuit components. A postive-going input pulse causes the cathodepotential of the lower cathode follower tube 164 to rise, .and anegative-going pulse causes the cathode potential of the upper cathodefollower tube 1112 to rise. At some time prior to time T the uppermultivibrator tube 126 is turned on and the lower multivibrator tube 128is cut off The relatively high anode voltage of the lower multivibratortube 128 is coupled back to the lower capacitor 112 so that the lowercapacitor 112 is discharging toward Zero. The relatively low anodevoltage of the upper multivibrator tube 126 is fed back to the uppercapacitor and is so low that the upper capacitor 110 charging toward thevoltage on the 30() volts bus 82. These charging and discharging pathsare indicated by the upper and lower capacitor voltage waves in FIGURE-5. Upon receipt of a positive-going input pulse at time T the lowercathode follower 104 applies a positive-going pulse through the diodenetwork 1% to the lower capacitor 112. This positive-going pulse servesto cause the .lower capacitor 112 to discharge quickly, as indicated bythe small spikeonits volt age wave at the time T Whenthe lowercapacitor112 is discharged, the lower coupling tube 122 is renderedconductive so that its cathode voltage rises. This rise' in voltage isapplied to the control grid of the lower multivibrator tube 128 which isturned, on. Through-typical multivibrator action, the uppermultivibratortube 126 is cut off, and hence its anode voltage becomes relativelyhigh. This relatively high voltage is coupled back through thepotentiometer 114 to the upper capacitor 110 so that the upper capacitor111) may then begin to discharge toward zero. The lower capacitor 112begins-to charge toward the voltage on. the 300 volts bus 82. T anegative-going pulse appearsat the input, and causes the upper cathodefollower'102 to provide a positive-going pulse to the upper capacitor110 and quicklydischarges is turned on and its cathode becomesrelatively positive At time to cause the upper multivibrator tube 126 tobe turned on. When the upper multivibrator tube 126 is turned on, thelower multivibrator tube 128 is cut off. When the lower multivibratortube 128 is cut off, its.anode voltage becomes relatively high which,when fed back through the lower potentiometer 116, permits the lowercapacitor 112 to begin to discharge toward zero. This operationcontinues, and the output pulses are derived through the discriminatorcircuit 130 and the output tube 134.

However, if at time T a pulse is lost, no positive-going pulse appearsat the cathode of the lower cathode follower tube 104w discharge thelower capacitor 112. Hence, the lower capacitor 112 continues todischarge until at some time slightly after time T the lower couplingtube 122 is turned on to cause the .lower multivibrator tube 128 to beturned on also. At this time, the upper multivibrator tube 126 is cutoff so that the upper capacitor 110 then begins to discharge towardzero. If at time T at negative-going pulse fails to appear, the uppercapacitor 110 continues to discharge and reaches some value at a timeafter time T which turns on the upper coupling tube 120. This causes theupper multivibrator tube 126 to turn on. At this time, the multivibratorswitches and the lower multivibrator tube 128 is cut off. Hence, thelower capacitor 112 begins to discharge toward zero. However, at time Tanother input pulse appears so that the lower capacitor 112 isdischarged at the proper time and the operation continues normally asexplained. Thus, it will be seen that the generator shown in FIGURE 4provides output pulses of the same frequency as the input pulses, and.provides output pulses of substantially the same frequency as the inputpulses just prior to their being lost or omitted. The time interval ofthe output pulses is determined by the previous length of time (wheninput pulses were present) during which time the timing capacitor hadbeen charging.

Another arrangement for allowing a programming control system to operatein the absence of input pulses is to limit the rate at which velocitycommands to the amplidyne field panel 34 can change. For example, if, inan information channel, a maximum acceleration of 1.5 inches per secondper second were imposed, and if pulses were lost for say 4 of a second,the maximum error encountered during such a loss would only be about0.005 of an inch. In accordance with the invention, a rate limit circuitmay be provided in the discriminator 38 shown in FIGURE 1. Thediscriminator 38 shown in the programmed system of FIGURE 1 is shown inblock diagram form in FIGURE 6. The discriminator shown in FIGURE 6,except for the rate limit circuit of the invention, is described in theabove-identified patents, and particularly in Patent No. 2,866,145.Briefly, the discriminator provides error signals for the programmedcontrol system in response to a comparison of signals indicative of theprogrammed position and signals indicative of the actual position.Signals indicative of the programmed position are derived from apreamplifier 36 and applied to a signal amplifier 140. Likewise, signalsfrom the selsyn 22 are applied to a selsyn signal amplifier 142. The twoamplified signals are applied to a phase discriminator 144 whichproduces a composite pulse having an average direct current valueindicative of the phase relationship of the two signals. These signalsare applied to an error signal clipper 146, after which they arefiltered in a filter 148. The filtered signals are then applied to therate limit circuit 150 in accordance with the invention, and thenapplied to a stabilizing circuit 152, and then to a neutral zone 154.Signals from the neutral zone 154 are applied to the amplidyne fieldpanel 34. Signals from the errorsignal clipper 146 are also applied,along with input signals from the preamplifier 36, to an excess errormonitor 156 which controls a relay 158 intended to cut off the system inthe presence of excessive error. A starting relay 160 is also-shown inthe discriminator, and must be appropriately energized in order toinitiate operation. Greater detailed explanation of the discriminatorshown in FIGURE 6 may be found in the Patent No. 2,866,145 as mentioned.However, the discriminator there described, does not include the ratelimit circuit in accordance with the invention. Briefly, the rate limitcircuit 150 is provided to limit the rate of change of signals derivedfrom the filter 148 before they are applied to the stabilizing circuit152.

FIGURE 7 shows a circuit diagram of one embodiment of the rate limitcircuit 150 which may be used in the discriminator 38. In FIGURE 7,signals from the filter 148 are applied to the control electrode of anamplifier triode tube 170. Signals are derived from a cathode followercircuit of the amplifier tube and applied to the stabilizing circuit152. These signals are also applied through a differentiating circuit172 and potentiometer 173 back to the control electrode of a feedbacktube 174. Signals are derived from the feedback tube 174 in a cathodefollower circuit and applied through a neutral zone diode network 176 toa reference resistor 17.7. These signals are compared to the voltageacross the reference resistor 177, and the difference is amplified in apentode tube 178. The output of the pentode tube 178 is a negativefeedback representative of the rate of change of the input signal (aspassed by the differentiating circuit 172). Hence, when this feedbacksignal is applied to the control electrode of the amplifier tube 170, itserves to limit the rate at which signals from the filter 148 maychange. The neutral zone network 176 is provided so as to limit thefeedback of voltages to those which exceed a predetermined level, namelythe conduction level of the diodes forming the neutral zone network 176.

FIGURE 8 shows another rate limiting circuit which is provided for thesame purpose as the rate limiting circuit of FIGURE 7. Signals from thefilter 158 are applied with respect to the ground bus 70 to a networkcomprising four rectifiers or diodes 190, 192, 194, 196, these diodesbeing connected in series pairs, and the pairs connected in parallel.The network is connected serially between the +300 volts bus 80 and the300 volts bus 82 by resistors 198, 200. Output signals are derived fromthe junction of one pair of diodes 194, 196. A capacitor 202 is coupledacross this output circuit. Input signals are applied to the junction ofthe other pair of diodes 190, 192. Normally, signals at the input of thecircuit shown in FIGURE 8 are at the same potential as signals at theoutput of the circuit. Current flows from the +300 v-olts bus 80 downthrough the resistor 198, splitting into the two diode branches anddownward through the resistor 200 to the +300 volts bus82. If the inputsignal applied to the circuit of FIGURE 8 were to increase rapidly in apositive direction, as it might in the absence of pulses or as it mightin response to a transient condition, it is desired to limit the signalswhich appear at the output so as to maintain as nearly normal operationas possible. If, as assumed, the signal input increased rapidly in apositive direction, the diode 192 would conduct an increased amount ofcurrent, and the diode would be cut 011. The junction of the diode 192and the resistor 200 would increase in a positive direction also andhence the diode 196 would be cut oif. Current from the +300 volts bus 80would then flow downward through the resistor 198 and the diode 194 andcharge the capacitor 202 at a rate determined by the value of thecapacitor 202 and the resistor 198. These values would be selected sothat the capacitor 202 would charge relatively slowly with respect tothe rapid increase in voltage at the input circuit so that the outputwill be changed only a relatively small amount. Once the capacitor wereappropriately charged, the circuit would attain its normal conditionwith all four diodes conducting substantially equal currents aspreviously. If the input voltage decreasedrapidly in a negativedirection, the opposite effect would take place with the diodes 192, 194

9 being cut off. The capacitor 202 would slowly discharge through thediode 196 and the resistor 260.

FIGURE 9 shows still another embodiment of the invention for limitingthe rate of change of signals from the filter 148 before these signalsare applied to the stabilizing circuit 152. The operation of the circuitof FIG- URE 9 is similar in principle to the operation of the circuit inFIGURE 8, inasmuch as the circuit of FIGURE 9 utilizes the outputcapacitor 292 for limiting the rate of change of the output voltage. Thecapacitor 202 is coupled between the ground bus 70 and the junction ofan NPN transistor 214 and a PNP transistor 216, these transistors 214,216 being serially coupled between buses 210, 212 of suitable potentialby resistors 218, 220-. The bases of the transistors 214, 216 arecoupled together and coupled to the input. Normally, some current isflowing through the series circuit comprising the resistor 218, the NPNtransistor 214, the PNP transistor 216 and the resistor 220. Any suddenchange in voltage at the input circuit causes one transistor to turn onmore fully and causes the other transistor to turn off by substantiallythe same amount. This condition serves, in effect, to either charge ordischarge the capacitor 202 depending upon the direction taken by thechange in input voltage. Thus, the circuit of FIGURE 9 provides asuitable rate limiting circuit utilizing transistors.

Although the invention has been described in specific embodiments andthe operation has been explained in what is considered to be the bestmodes of operation, it is to be understood that the embodiments shownand described are merely illustrative, and that the invention is notlimited to such embodiments or operation since alterations and changeswill suggest themselves to persons skilled in the art, such changes andalterations being within the spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a system for developing a plurality of alternating electricalsignals from a single source, said plurality of alternating electricalsignals having similar electrical qualities and a predetermined phaserelationship; said system having means for integrating square wavesignals, waveshaping means coupled to said integrating means for formingsaid integrated signals into desired signals, and means including aphase shift device and a transformer coupled to said wave-shaping meansfor deriving at least two output signals having said predetermined phaserelationship; the improvement comprising square wave producing meansadapted to be coupled to said source and to said integrating means, saidsquare wave producing means being capable of producing said square wavesignals normally in response to said source signals and further beingcapable of producing square wave signals of a predetermined frequency inthe absence of said source signals.

2. In a system for developing a plurality of alternating currentelectrical signals having similar electrical qualities and'apredetermined phase relationship; said system having a source ofreference signals, means for integrating rectangular wave signals,wave-shaping means coupled to said integrating means for forming firstsubstantially sinusoidal wave signals from said integrated signals,phase shifting means coupled to said wave-shaping means for producingsecond substantially sinusoidal wave signals having a shifted phaserelative to the phase of said first sinusoidal wave signals, andtransformer means coupled to said phase shifting means and to saidwave-shaping means for producing two output alternating currentelectrical signals therefrom, said output signals having saidpredetermined phase relationship and said similar electrical qualities;the improvement comprising means adapted to be coupled between saidsource and said integrating means for producing substantiallyrectangular waves in response to said reference signals and producingsquare waves of a predetermined frequency in the absence of saidreference signals.

3. In a program control system wherein a reference control pattern isstored on a data storage medium, said system having first means coupledto said storage medium for'deriving reference electrical signalstherefrom to synchronize a device that reproduces said pattern, secondmeans for integrating rectangular wave electrical signals, third meanscoupled to said second means for producing first substantiallysinusoidal alternating current electrical signals from said integratedsignals, additional circuit means coupled to said first, second, andthird means for producing second substantially sinusoidal alternatingcurrent electrical signals, and transformer means coupled to said thirdmeans and to said additional circuit means for deriving at least twooutput electrical signals therefrom; the improvement comprising fourthmeans adapted to be coupled between said first and second means forproducing rectangular wave alternating current electrical signals inresponse to said reference electrical signals and producing rectangularwave signals having a predetermined frequency in the absence of saidreference electrical signals.

4. In a program control system having a reference pattern stored on adata storage medium, means coupled to said data storage medium forderiving reference signals therefrom, means for integrating square wavealternating signals, means coupled to said integrating means forproducing substantially sinusoidal alternating current signals inresponse to said integrated signals, first amplifying means coupled tosaid sinusoidal producing means for amplifying a portion of saidsubstantially sinusoidal alternating signals, means coupled to saidsinusoidal producing means for shifting the phase of another portion ofsaid substantially sinusoidal alternating signals, second amplifyingmeans coupled to said phase shifting means for amplifying the phaseshifte-d'portion of said substantially sinusoidal alternating signals,and transformer means respectively coupled to both said amplifying meansfor producing substantially sinusoidal alternating current signalshaving predetermined phase relationships with each other; theimprovement comprising multivibrator means adapted to be coupled betweensaid deriving means and Said integrating means for producing square wavealternating signal-s, said multivibrator means being capable ofproducing square wave alternating signals in response to said referencesignals and being capable of producing square wave alternating signalsof a predetermined frequency in the absence of said reference signals.

5. In a program control system for controlling object motion wherein achannel of reference information and at least one channel of controlinformation are stored in a data storage medium in the form ofelectrical signals having a phase relationship representative of theobject motion, wherein first means are coupled to said control channelfor deriving signals therefrom, and wherein discriminator means areprovided for producing error signals for controlling said object motion;the improvement comprising generating means adapted to be coupled tosaid first deriving means and to said discriminator means for producingcontrol signals in response to said derived signals and for producingcontrol signals of predetermined characteristics in the absence of saidderived signals.

6. In a programmed control system wherein a reference channel ofinformation and at least one control channel of information are storedin a data storage medium in the form of electrical signals having aphase relationship representative of the programmed operation, whereinfirst means are coupled to said control channel for deriving controlsignals therefrom, wherein second means are coupled to said referencechannel for deriving reference signals therefrom, wherein discriminatormeans are coupled to said second deriving means for producing errorsignals indicative of the phase relationship of control signals and saidderived reference signals, and wherein operating means are coupled tosaid discriminator means for con- Ill trolling the operation of anobject in response to said error signals; the improvement comprisinggenerating means adapted to be coupled between said'first deriving meansand said discriminator means for producing cont-r01 signals of acharacteristic similar to and in response to said derived controlsignals and for producing control signals. of a predeterminedcharacteristic when said derived control signals are faulty.

7. In a system for controlling the motion of an object wherein areference channel of information and at least one control channel ofinformation are stored in a data storage medium and each channel isavailable in the form of electrical signals having a phase relationshiprepresentative of the desired object motion, wherein first means arecoupled to said control channel for deriving control signals therefrom,wherein second means are coupled to said reference channel for derivingreference signals therefrom, wherein third means are provided forgenerating signals indicative of the actual motion of said object,wherein discriminator means are coupled to said third means forproducing error signals indicative of the phase relationship ofsaidactual operating signals and control signals, and wherein operatingmeans are coupled to said discriminator means for controlling the motionof said object in response to said error signals; the improvementcomprising generating means adapted to be coupled to said first derivingmeans and to said discriminator means for supplying control signals tosaid discriminator means, said control signals having a characteristicsimilar to said derived control signals and being produced in responseto said derived control signals, and for supplying control signals of apredetermined characteristic to said discriminator means during the timesaid derived control signals are faulty.

8. The position control system as defined in claim 7, wherein saidgenerating means include a multivibrator for producing said controlsignals in response to said derived control signals and further includetiming circuits coupled to said multivibrator for timing the operationof said multivibrator as determined by said derived control signalsprior to their becoming faulty.

9. In a control system having means for developing electrical signalsindicative of the condition of an object being controlled, a source ofcontrol electrical signals, and comparator means for developing an errorsignal indicative of the phase relationship of said condition indicatingsignals and said control signals, the improvement comprising meansadapted to be coupled to said comparator means for limiting the rate ofchange of said error signal and for producing output signals in responseto said limited error signal.

10. In a control system wherein a reference channel of information andat least one control channel of information are stored in a data storagemedium and each channel is available in the form of electrical signalshaving a phase relationship representative of a desired operation,wherein means are provided for developing signals representative of theactual operation of said system, and wherein means are provided forcomparing the phase relationship of said actual signals and controlsignals derived from said one control channel and for developing anerror signal proportional to said phase relationship; the improvementcomprising means adapted to be coupled to said comparing means forlimiting the rate of change of said error signal, amplifying meanscoupled to said limiting means, and means coupled to said amplifyingmeans for producing control signals therefrom.

11. A control system as defined in claim 10, wherein said means forlimiting comprises a negative feedback circuit and a differentiatingcircuit for limiting the rate of change of said error signal.

12. The control system as defined in claim 10, wherein said limitingmeans comprises a capacitor, and means associated therewith for chargingor discharging said capacitor at a predetermined rate and therebylimiting said rate of change of said error signal.

No references cited.

IRVING L. SRAGOW, Primary Examiner.

1. IN A SYSTEM FOR DEVELOPING A PLURALITY OF ALTERNATING ELECTRICALSIGNALS FROM A SINGLE SOURCE, SAID PLURALITY OF ALTERNATING ELECTRICALSIGNALS HAVING SIMILAR ELECTRICAL QUALITIES AND A PREDETERMINED PHASERELATIONSHIP; SAID SYSTEM HAVING MEANS FOR INTEGRATING SQUARE WAVESIGNALS, WAVE SHAPING MEANS COUPLED TO SAID INTEGRATING MEANS FORFORMING AND INTEGRATED SIGNALS INTO DESIRED SIGNALS, AND MEANS INCLUDINGA PHASE SHIFT DEVICE AND A TRANSFORMER COUPLED TO SAID WAVE-SHAPINGMEANS FOR DERIVING AT LEAST TWO OUTPUT SIGNALS HAVING SAID PREDETERMINEDPHASE RELATIONSHIP; THE IMPROVEMENT COMPRISING SQUARE WAVE PRODUCINGMEANS ADAPTED TO BE COUPLED TO SAID SOURCE AND TO SAID INTEGRATINGMEANS, SAID SQUARE WAVE PRODUCING MEANS BEING CAPABLE OF PRODUCING SAIDSQUARE WAVE SIGNALS NORMALLY IN RESPONSE TO SAID SOURCE SIGNALS ANDFURTHER BEING CAPABLE OF PRODUCING SQUARE WAVE SIGNALS OF APREDERTERMINED FREQUENCY IN THE ABSENCE OF SAID SOURCE SIGNALS.